Recently, a semiconductor laser apparatus, which is capable of achieving a high output power of several to 100 W, has been developed. Such a semiconductor laser apparatus is also used as a light source of, for example, a laser knife, a laser soldering iron, and a laser marker.
Since the electro-optical conversion efficiency of a semiconductor laser array is about 50%, half of the input power is to be converted into heat. Such heat has a great impact on laser output power, efficiency, and element lifetime. In order to effectively cool such heat, used is a heat sink that employs water, which have a high thermal conductivity as well as a high heat capacity, as a refrigerant. As such a heat sink, known is one, for example, having a structure in which a plurality of copper plate-shaped members are combined to form a fine flow path and cooling water is circulated in the flow path. The cooling water is adapted to exchange heat with the semiconductor laser array placed on the flow path to cool the semiconductor laser array (refer to Patent Documents 1 and 2, for example).
Such a semiconductor laser apparatus as mentioned above has a stack structure in which a plurality of semiconductor laser arrays are stacked. In the case of achieving a higher output power, a plurality of heat sinks are to be inserted, respectively, between the stacked semiconductor laser arrays. Since these heat sinks are adapted not only to cool the semiconductor laser arrays but also to serve as an electrical conduction path between the semiconductor laser arrays, an electric field is to be applied also to the heat sinks during the operation of each semiconductor laser array (refer to FIG. 1 in Patent Document 1, for example).                Patent Document 1: International Patent Publication No. WO00/11717        Patent Document 2: Japanese Published Unexamined Patent Application No. H10-209531        